Relating to texturizing protein, many methods have heretofore been known. For example, as a method of forming the fibrous structure and removing bad-smelling fragments, there is known a spinning process wherein an alkaline aqueous solution of protein is forced into a coagulation bath through an orifice.
Although this technique is superior in providing good fibrous texture and in deodorization, it requires several chemicals for the process and the process is complicated, and therefore it cannot be said to be an economical method. Relating to the above, as an economical method there has been known an extruding system, and relating to this method many improvements have been proposed. One of these is a method wherein a protein raw material containing about 15-40% of moisture is subjected to a pressing and heating treatment in an extruder, and then it is released through an orifice into the atmosphere thereby allowing it to expand and be texturized under water vapor pressure at the time of release thereof. This method has an advantage that its process is simple and produces the textured protein at a lower cost, however there is still a difficulty that most of bad-smelling fragments originating from the raw material are left as they are, and also there are many difficulties relating to the taste.
Moreover, recently there has been proposed a method of making a reticulated textured structure by use of water vapor. For example, Japanese patent application laying-open No. 15853/77 in such a method that an aqueous liquid coating protein is introduced into a restricted treating area and steam is injected therein, thereby reticulating and texturizing the protein, and Japanese patent application publication No. 6665/74 discloses a method wherein an aqueous liquid containing protein is forcibly caused to directly contact with steam through an ejector thereby causing denaturation by heating under the fluidized condition to produce the fibrous structure. However, neither method can be said to be preferable because in both methods steam is used in the open condition at a higher temperature, namely it is not preferable to release the pressure from a pressurized condition to the atmosphere in view of thermal efficiency considerations and also the operation thereof.
Moreover, in the method of Japanese patent application laying-open No. 88657/76, an aqueous liquid containing protein is subjected to a preheating treatment at a temperature above 30.degree. C. and below a temperature which causes the gelatinization thereof, and then the thus treated material is extruded into a water bath of 90.degree.-99.degree. C. thereby completely causing the gelatinization and thus resulting in forming the fibrous structure. Japanese patent application publication No. 25535/75 discloses a method wherein an aqueous liquid containing protein is heated at a temperature above 74.degree. C. in a tubular heat exchanger and then is released from the pressurized heated condition above 3.5 kg/cm.sup.2 (50 psig) into the air or water under the atmospheric pressure. Even if the above two methods are used, the removal of the bad-smelling fragments originating from the raw material is insufficient, and therefore there is still a large difficulty in this respect.